I may be wrong, but Germany does not have any public waters where you can just decide to go fishing. There is a pretty drawn out process to get licensed as well as a slew of other rules. Here is a link that may help answer your questions:

Kelly's got it right! Very strict rules and enforcement! Learned the hard way in the 70s when a farmer told my German speaking gf that I could fish a lake near Bremeraven. I was wondering why all the guys with euro tackle on the banks were staring at me fly fishing and releasing Bach Forellen (Brown Trout the only German word I knew beside beer!).then the constable came and wanted to lock me up!Still don't know what went wrong to this day but that was my extent of German fishing!

__________________
"I was born to fish" Lee Wulff
"There's more B.S. in fly fishing then there is in a Kansas feedlot." Lefty Kreh
" It ain't over till it's over." Yogi Berra
"Your not old,you've simply acquired a patina." Swirlchaser

Kelly's got it right! Very strict rules and enforcement! Learned the hard way in the 70s when a farmer told my German speaking gf that I could fish a lake near Bremeraven. I was wondering why all the guys with euro tackle on the banks were staring at me fly fishing and releasing Bach Forellen (Brown Trout the only German word I knew beside beer!).then the constable came and wanted to lock me up!Still don't know what went wrong to this day but that was my extent of German fishing!

Today, C&R is basically banned in Germany, but I don't know what the situation was in the 70s. Maybe you strolled up to the wrong lake.

In Switzerland we have a similar law. Fishing with the "intent" to catch and release a fish isn't allowed. How someone determines that intent is beyond me. Releasing fish that are undersized or protected is the law, but you can also release non-targeted species and fish for "ecological reasons". The only fish you are absolutely required to kill are non-natives (rainbows, sunfish, etc.)

Honestly, if I were going to Germany, wanted to spend a day fishing, and I didn't speak German, I'd probably just go ahead and hire a guide. I find it all confusing enough and I'm fluent...